Me too, won't allowed my cat go outside unattended. I'm afraid he'd eat trash, get lost, or could get hurt by other cats or by humans.

Somehow cats seem like understand what we're saying. Whenever I let my cat play outside (under my supervision), I told him he had 20-30 minutes to play outside and had to be back at (say) 10.30. Surprisingly, he will return home voluntarily at the appointed hour. Maybe it's just a coincidence, but it's happened several times.